Population rhythms are exhibited by different parts of the brain under different behavioral conditions. Of special interest, several characteristic oscillatory patterns appear during sleep and epilepsy. Investigation of sleep oscillations may illuminate the role of sleep in mammals and increase our understanding about the effects of different drugs on different sleep stages. In addition, studying these rhythms as relatively simple activity states leads to new understanding about cells, synapses and circuitry. This information is important for understanding brain functions during information processing. We have investigated the spindle oscillations observed during light sleep and anesthesia, and propose to continue this investigation and relate it to other kinds of oscillations such as delta rhythms observed during slow-wave or deep sleep and absence seizures related to petit mal epilepsy.